Concrete Block Calculation Formula
Block Area = ((Block Length + Mortar Thickness) ÷ 1000) × ((Block Height + Mortar Thickness) ÷ 1000)
Blocks Required = Wall Area ÷ Block Area
Blocks with Waste = Blocks Required × (1 + Waste Allowance ÷ 100)
Cement Bags Required = Blocks with Waste ÷ 10
Sand Bag (m³) = (Blocks with Waste × Block Length × Block Height × Mortar Thickness) ÷ 1,000,000,000
Total Cost = Blocks with Waste × Block Price (if provided)
Standard Block: 400mm × 200mm (default dimensions)
Cement Ratio: 10 blocks per bag of cement
Sand Bag: Calculated in cubic meters (m³) based on block dimensions and mortar thickness
Note: All dimensions include mortar thickness for accurate calculations
Quick Answer: How Many Besser Blocks Per m²?
Standard 390mm × 190mm besser blocks (with 10mm mortar joints) require 12.5 blocks per square metre of wall. This applies to all standard wall blocks per AS 4455.1, including 190mm and 290mm series. Width only changes core fill volume, not block count.
Quick formula: Wall length (m) × Wall height (m) × 12.5 = block count. Add 5–10% wastage.
For exact quantities including mortar bag count, use the calculator above.
Related Resources
Concrete Block Calculator — How Many Blocks for Your Wall?
Calculate concrete block quantities for walls, retaining walls, and fences. Works with standard Australian block sizes: 90mm, 140mm, 190mm, and 290mm series.
Blocks Per Square Metre
| Block Size | Dimensions | Blocks per m² |
|---|---|---|
| 90mm series | 390 x 90 x 190mm | 12.5 |
| 140mm series | 390 x 140 x 190mm | 12.5 |
| 190mm (besser) | 390 x 190 x 190mm | 12.5 |
| 290mm series | 390 x 290 x 190mm | 12.5 |
Frequently Asked Questions
How many concrete blocks per square metre?
All standard Australian concrete blocks (390mm long x 190mm high with 10mm joints) require 12.5 blocks per square metre, regardless of width. The width only affects cost and core fill volume.
How many besser blocks do I need for a retaining wall?
Calculate the wall face area (length x height) and multiply by 12.5. For a 5m long, 1.2m high retaining wall: 5 x 1.2 = 6m² x 12.5 = 75 blocks. Add 5% for waste = 79 blocks.
What is the difference between a besser block and a concrete block?
They are the same thing. Besser is a brand name that became the generic term in Australia, like how Esky means cooler. The correct term is concrete masonry unit (CMU).
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Helpful Guides
How Many Concrete Blocks Do I Need?
How many concrete blocks per m²?
For standard 390mm x 190mm besser blocks (10mm mortar joint), you need 12.5 blocks per m². For 290mm wide blocks, the count stays the same since the face dimensions are identical — width only affects core fill volume.
How many concrete blocks for a wall?
Multiply wall length × height (in metres) by 12.5. For example, a 6m × 2.4m wall = 14.4 m² × 12.5 = 180 blocks. Add 5-10% wastage for cuts and breakages — round up to ~190 blocks.
Cemex block calculator — what size?
Cemex (and Boral, Adbri Masonry) blocks all conform to AS 4455.1 face dimensions. Whether you specify Cemex 190 series or Boral GB Smooth, the block-per-m² calculation is identical: 12.5 blocks/m² for standard wall blocks.
How many blocks for a retaining wall?
For standard hollow-core retaining walls under 1m high, calculate face area × 12.5, then add a course-and-a-half for the buried foundation row. Walls over 1m require engineering — most use 190 or 290 series with full core fill (see our core fill calculator).
Block calculation formula
The formula is: Blocks = (Wall Length × Wall Height) ÷ Block Face Area × Wastage Factor. With AS 4455 blocks (390 × 190 mm face including 10mm joint), one block face = 0.08 m². Therefore Blocks per m² = 1 ÷ 0.08 = 12.5. Apply 1.05-1.10 wastage factor depending on cut complexity.
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